Value-bearing documents, such as tickets, building permits, gift certificates, etc., must be issued to requesters and validated by validators in an efficient and secure manner. For example, in ticket generation/validation systems, there must be some mechanism to prevent counterfeiting without unduly burdening the ticket validator. Accordingly, some document generation/validation systems encrypt some or all of the information in a ticket to provide security.
One problem with the use of encryption in existing document generation/validation systems is that these systems rely on a single encryption key or key pair to encrypt and validate documents. For example, in a document generation/validation system that uses symmetric encryption, a single key is used to encrypt and to validate all of the documents. If the single key is compromised, all of the documents encrypted using the single key are compromised and must be reissued. For example, in an electronic ticketing system in which all tickets are issued under the same key, and that key is deciphered by a counterfeiter, reissuing all of the tickets under a new key is required. As a result, in single-key document generation/validation systems, strong encryption algorithms and long key lengths are used to reduce the likelihood of compromise. Using strong encryption algorithms and long key lengths increases the computational burden on the entity that generates the encrypted document and the document validator.
Another problem with using a single key or key pair to validate documents is that the encryption cannot be varied to suit the needs of a particular issuer. For example, an issuer of $10 gift certificates may not be as concerned about the loss of an encryption key as the issuer of $1000 gift certificates. However, because a single key is used, the same level of encryption must be applied in both instances. Thus, conventional document generation/validation systems lack the flexibility to meet individual issuer's or issuers' needs.
Accordingly, there exists a long felt need for improved methods and systems for generating and validating value-bearing documents.